A lapping machine is generally employed for lapping accurately a surface of an object such as a silicon substrate to be employed for manufacturing an integrated circuit or an alumina-titanium carbide substrate to be employed for manufacturing a magnetic head.
FIG. 4 is a front view of a typical structure of the conventionally employed lapping machine, and FIG. 5 is a top view of the lapping machine of FIG. 4. The lapping machine of FIGS. 4 and 5 comprises a lapping board 43 which is fixed to an axis of rotation 42 of a motor 41, a abrasive grain-supplying means 45 which supplies a slurry 44 containing abrasive grains on the surface of the lapping board 43, and disc means 47 for rotatably supporting an object 46 to be lapped.
The object 46 is temporarily attached to the supporting means 47 via wax or the like. The supporting means 47 is supported on its circumferential side with a pair of rollers 50. Each roller 50 is rotatably supported by a roller-supporting means 53 which is arranged on the top of a pole 22 standing on a base board 51.
The lapping board 43 rotates in the direction indicated by the arrow 49 (see FIG. 5) by activating the motor 41. With the rotation of the lapping board 43, the supporting means 47 holding the object 46 rotates under guidance with the pair of rollers 50.
On the surface of the lapping board 43, the abrasive grain slurry 44 is dropwise supplied from the abrasive grain-supplying means 45. Abrasive grains generally are diamond grains, alumina grains, or silica grains. The abrasive grain slurry 44 is moved toward the object 46 and supplied between the lapping board 43 and the object 46 by the rotation of the lapping board 43.
The lapping board 43 temporarily holds abrasive grains between the object 46 and the board 43. Thus, the lapping board 43 is generally made of relatively soft material such as tin, as compared with the abrasive grains. For instance, a lapping board made of tin is slightly deformed on its surface to temporarily hold the abrasive grains.
When the lapping board 43 and the object to be lapped 46 are independently rotated with the intervening abrasive grains, the under-surface of the object 46 is polished. The polishing using abrasive grains is generally named “lapping”.
JP-7-299737 A describes that the conventionally used lapping method such as that described above sometimes produces unfavorable recesses and scratches on the lapped surface of the object, particularly electric devices having a soft metal area and hard metal area on their surfaces. According to the descriptions, the recesses and scratches are produced mainly by the presence of free abrasive grains unfixed onto the lapping board. Then, this JP publication proposes a lapping method utilizing previously abrasive grain-embedded lapping board which is manufactured by the steps of supplying a slurry of abrasive grains in a liquid medium onto a lapping board, fixing some of the supplied grains onto the lapping board under the partly embedded condition, and removing unfixed abrasive grains from the lapping board.
The above-identified lapping board on which abrasive grains are previously fixed under the partly embedded condition is theoretically satisfactory because the lapping board has no unfixed abrasive grains on its surface.
The present inventor has noted that the manufacturing procedure of the lapping board described in the JP publication has a drawback in that it takes a long period of time to manufacture a lapping board onto which an appropriately great number of abrasive grains are uniformly fixed. Because of this drawbacks, the manufacturing method of JP publication is hardly applicable in industry.